The Five Carburetor Circuits: Interdependency

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Interdependencies–what the heck is that? Well…read on… I know I had to.

Do you wonder about interdependencies? Me too!

a. Although the five circuits of the carburetor have been treated independently for the

purpose of simplifying the explanation, a word of caution is advisable here as to the interdependency of the different circuits. If the float circuit is not up to standard, the supply of fuel for the operation of the low speed, high speed, and pump circuits will be affected, and hence the operation of all three circuits may be hampered. It has been pointed out that the operation of the low speed circuit does not cease when the high speed circuit starts to function. Similarly, in some cases, notably on units built for Chevrolet Motor Company, since 1934 there is an interdependency between the high speed and pump circuits. On these units the pump circuit delivers a small quantity of fuel at part throttle and higher engine speeds, although the throttle is held steady and the pump plunger is not in motion. This is called “pump bleed” or “pump pull-over,” and the unalterably designed feature of this pump permits it to discharge this fuel in the same manner as fuel is discharged from the high speed circuit. When the unit is properly serviced, this built-in feature will take care of itself.

b. The interdependency of the circuit is not emphasized to add technical confusion to the mind of the service man, but rather to show that, for the absolute precision operation, of which the carburetor is capable, all five circuits must be carefully serviced. No snap judgment should be made in diagnosing carburetor trouble, and no “favorite” should be played when circuits are serviced.